The present invention relates to a power booster for vehicle brake systems. More particularly, the invention relates to a vacuum power booster which uses vacuum and atmospheric pressure to provide power assist to a fluid brake system's master cylinder.
Power boosters operating on vacuum pressure are well known and generally comprise a piston which is axially moveable by differential pressures acting on a diaphragm and support plate which separate the booster housing into a control volume containing vacuum and a control volume containing a variable pressure. A valve mechanism for the power booster is operable to admit atmospheric air pressure into the control volume containing variable pressure to actuate the power booster and move the piston.
It is known to provide a tie rod which extends through a power booster and penetrates the diaphragm and support plate to transmit forces which act upon the booster housing. This type of an arrangement requires a complex sealing structure between the tie rod and the diaphragm and does not provide direct support to the power piston itself. It is also known to provide an axial force transmission unit which extends through the valve mechanism. This type of an arrangement is not amenable to the use of a conventional valve mechanism with the booster which instead must be replaced by a new and complex valve design.